Google Chrome项目中实现了WebRTC并提供了示例，WebRTC提供了视频会议的核心技术，包括音视频的采集、编解码、网络传输、显示等功能，并且还支持跨平台：windows，linux，mac，android。Chrome是开源的，提供了视频会议示例（基于摄像头），也有屏幕截图组件（全屏、窗口），但是没有屏幕分享的例子，搜了百度、谷歌、github都没有。在Google论坛找到了关键的图像转视频流后实现了此模块。

在72版本测试通过，有同事在53版本也可以。

代码如下：

MyCapturer.h

/**
*　Windows屏幕录像模块
*/

#include <media/base/videocapturer.h>
#include <media/base/videocommon.h>
#include <modules/desktop_capture/desktop_capturer.h>
#include <modules/desktop_capture/desktop_frame.h>
#include <api/video/i420_buffer.h>
#include <api/scoped_refptr.h>
#include <rtc_base/messagehandler.h>
#include <rtc_base/thread.h>

class MyCapturer : public cricket::VideoCapturer,
                   public rtc::MessageHandler,
                   public webrtc::DesktopCapturer::Callback {
 public:
  MyCapturer();
  ~MyCapturer();

  void CaptureFrame();

  virtual cricket::CaptureState Start(
      const cricket::VideoFormat& capture_format);
  virtual void Stop();
  virtual bool IsRunning();
  virtual bool IsScreencast() const { return true; }
  virtual void OnCaptureResult(webrtc::DesktopCapturer::Result result,
                               std::unique_ptr<webrtc::DesktopFrame> frame);
  virtual void OnMessage(rtc::Message* msg);

 protected:
  virtual bool GetPreferredFourccs(std::vector<uint32_t>* fourccs);

 private:
  std::unique_ptr<webrtc::DesktopCapturer> capturer;
  rtc::scoped_refptr<webrtc::I420Buffer> i420_buffer_;
};

MyCapturer.cc

#include "MyCapturer.h"
#include <base/threading/thread.h>
#include <modules/desktop_capture/desktop_capture_options.h>
#include <third_party/libyuv/include/libyuv.h>

MyCapturer::MyCapturer() {
  std::vector<cricket::VideoFormat> formats;
  formats.push_back(cricket::VideoFormat(
      800, 600, cricket::VideoFormat::FpsToInterval(30), cricket::FOURCC_I420));
  SetSupportedFormats(formats);
}

MyCapturer ::~MyCapturer() {}

cricket::CaptureState MyCapturer::Start(
    const cricket::VideoFormat& capture_format) {
  cricket::VideoFormat supported;
  if (GetBestCaptureFormat(capture_format, &supported))
    SetCaptureFormat(&supported);
  SetCaptureState(cricket::CS_RUNNING);
  auto options = webrtc::DesktopCaptureOptions::CreateDefault();
  options.set_allow_directx_capturer(true);
  capturer = webrtc::DesktopCapturer::CreateScreenCapturer(options);
  capturer->Start(this);
  CaptureFrame();
  return cricket::CS_RUNNING;
}

void MyCapturer::Stop() {
  SetCaptureState(cricket::CS_STOPPED);
  SetCaptureFormat(NULL);
}

bool MyCapturer::IsRunning() {
  return capture_state() == cricket::CS_RUNNING;
}

bool MyCapturer::GetPreferredFourccs(std::vector<uint32_t>* fourccs) {
  fourccs->push_back(cricket::FOURCC_I420);
  fourccs->push_back(cricket::FOURCC_MJPG);
  return true;
}

void MyCapturer::OnCaptureResult(webrtc::DesktopCapturer::Result result,
                                 std::unique_ptr<webrtc::DesktopFrame> frame) {
  if (result != webrtc::DesktopCapturer::Result::SUCCESS)
    return;

  int width = frame->size().width();
  int height = frame->size().height();

  if (!i420_buffer_.get() ||
      i420_buffer_->width() * i420_buffer_->height() < width * height) {
    i420_buffer_ = webrtc::I420Buffer::Create(width, height);
  }
  libyuv::ConvertToI420(frame->data(), 0, i420_buffer_->MutableDataY(),
                        i420_buffer_->StrideY(), i420_buffer_->MutableDataU(),
                        i420_buffer_->StrideU(), i420_buffer_->MutableDataV(),
                        i420_buffer_->StrideV(), 0, 0, width, height, width,
                        height, libyuv::kRotate0, libyuv::FOURCC_ARGB);

  OnFrame(webrtc::VideoFrame(i420_buffer_, 0, 0, webrtc::kVideoRotation_0),
          width, height);
}

void MyCapturer::OnMessage(rtc::Message* msg) {
  if (msg->message_id == 0)
    CaptureFrame();
}

void MyCapturer::CaptureFrame() {
  capturer->CaptureFrame();

  rtc::Location loc(__FUNCTION__, __FILE__);
  rtc::Thread::Current()->PostDelayed(loc, 33, this, 0);
}

将这个类加入peerconnection/client工程后，在Conductor::AddTracks()中调用，将

std::unique_ptr<cricket::VideoCapturer> video_device = OpenVideoCaptureDevice();

修改为

std::unique_ptr<cricket::VideoCapturer> video_device = std::unique_ptr<cricket::VideoCapturer>(new MyCapturer());